Analysis of the pattern of QM expression during mouse development

QM, a novel gene that was originally identified as a putative tumor suppres sor gene, has since been cloned from species encompassing members of the pl ant, animal, and fungal kingdoms. Sequence comparison indicates that QM has been highly conserved throughout eukaryotic evolution. QM is a member of a multigene family in both mouse and man, is expressed in a broad range of t issues, and is downregulated during adipocyte differentiation. Jif-1, a chi cken homolog of QM, has been reported to interact with the protooncogene c- Jun, and to inhibit transactivation of AP-1 regulated promoters in vitro. F urther mon, disruption of the yeast QM homolog is lethal. Although these st udies suggest that the QM gene product plays an important role within the n ormal cell, the precise role of QM has remained elusive. In this study, a t horough analysis of the pattern of QM expression during mouse development w as undertaken, using the techniques of whole mount in situ hybridization an d whole mount immunohistochemistry, in combination with conventional immuno histochemical analysis of tissue sections. QM is expressed in numerous embr yonic tissues, and is differentially expressed throughout the embryo. The c ytoplasmic localization of QM is consistent with its reported association w ith ribosomes, and inconsistent with its previously hypothesized function a s a direct modulator of the nuclear protooncogene c-Jun. QM is expressed in the developing epidermis, and is particularly strong within developing lim bs. Analysis of embryos of various stages of gestation indicate that QM is downregulated in the surface ectoderm of the embryo as development proceeds . QM protein is not detectable within either nucleated or enucleated red bl ood cell precursors. QM is strongly expressed within chondrocytes within th e transition zone of developing limb cartilage, as well as within different iated keratinocytes of the suprabasal regions of the epidermis. Furthermore , within both cartilage and skin, there is an inverse relationship between QM expression and proliferative capacity. This pattern of QM expression sug gests that this novel gene product may be involved in processes such as pos ttranslational protein processing which are essential for differentiation o f specific tissues during embryogenesis.